The fire whirl

A fire whirl from a liquid-fuel pool (acetone) is formed at the center of a rotating screen which imparts a controlled angular momentum to the ambient air. Measurements show that outside of the core the fluid motion is that of a free vortex. A hot-wire method of measurement of the radial temperature distribution is developed. The temperature distribution shows that the fire whirl consists of a rotating cylinder, fuel rich inside, lean outside. The turbulent plume theory is extended to include combustion and angular momentum. This theory checks the experimental results and provides: o 1. The turbulent mixing coefficient decreases with increasing angular momentum, as is to be expected. 2. The turbulent mixing coefficient increases with elevation above the ground. This effect was not expected. Its cause remains unknown, although it may be in some way related to the vertex-jump (vortex breakdown) phenomena which may be required if the whirl is to satisfy both ground-level and “high”-altitude boundary conditions.